Investigations in acne

In most cases of acne, no tests are necessary.

However, occasionally it is wise to obtain a swab from an acne lesion for microbiological examination and culture to determine whether:

• Bacteria, especially Proprionibacterium acnes, are sensitive to the prescribed antibiotics
• There are Gram negative bacteria or Staphylococcus aureus causing folliculitis
• There are yeasts such as Malasezzia (Pityrosporum ovale) causing malassezia folliculitis or seborrhoeic dermatitis
• There are fungi such as Trichophyton rubrum causing facial tinea

Some women may be advised to have blood tests to measure hormone levels. The reasons include:

• Possibility of pregnancy, which would influence what treatment was appropriate
• Signs suggesting high levels of male sex hormones, which could be due to conditions such as polycystic ovaries or congenital adrenal hyperplasia
• Signs suggesting excessive prolactin
• Signs suggesting Cushing's syndrome

These hormone tests are best taken between 8:00 and 10:00 am during the first half of the menstrual cycle. They may include:

• Testosterone
• Sex hormone binding globulin (SHBG)
• Free androgen index (FAI)
• Dehydroepiandrosterone sulphate (DHEAS)
• 17-hydroxyprogesterone
• Synacthen test of adrenal stimulation by adrenocorticotrophic hormone (ACTH)
• Luteinising hormone (LH) & Follicular Stimulating Hormone (FSH)
• Prolactin
• Cortisol
• Dexamethasone suppression test

A pelvic ultrasound scan is usually very good at excluding ovarian cysts and tumours on the ovary and adrenal gland.

Tests during treatment

Blood tests may be performed to monitor the safety of treatment:

• Full blood count (especially if the patient is unwell)
• Liver function in those on antibiotics or isotretinoin
• Fasting lipids (cholesterol and triglyceride) in those on isotretinoin.
• Beta human chorionic gonadotrophin or hcg (pregnancy test) in those on isotretinoin.